Like millions of other American parents, my husband and I received a warning letter from the BMI police last week. Our active, healthy 8th-grade daughter is “very lean,” according to her school-administered “Fitnessgram.” The national student body monitors think this is a public health problem.

The obesity report card lectured that because our daughter’s body-mass index is “very low,” we “should make certain” that she “is eating a healthy diet that includes the appropriate number of calories.” Thanks, geniuses. We had no idea such measurements were taking place, and we wondered whether we were alone in objecting to this unsolicited Nanny State dispatch. We’re not.

In New York, mom Laura Williams blew the whistle on how her perfectly healthy daughter Gwendolyn was branded “overweight” by her Fitnessgram. City schools sent the reports home to nearly 900,000 students in their backpacks. Gwendolyn showed the assessment to the New York Post last week, exclaiming: “I’m 4-foot-1, and 66 pounds, and I’m like, what?!”

Thanks to the Williams family’s whistleblowing and a huge public backlash, Big Apple schools will now change the way the fitness reports are distributed to families. But changing the delivery route doesn’t address the expansive government encroachment on our children’s health based on dubious science.

Gwendolyn’s absurd classification exposes the unreliability of BMI ratings, which many public health scientists admit are inadequate health predictors. The Centers for Disease Control itself says that “the accuracy of BMI varies substantially according to the individual child’s degree of body fatness” and doesn’t distinguish between “excess fat, muscle or bone mass, nor does it provide any indication of the distribution of fat among individuals.”

Yet some school districts have pushed to incorporate BMI results in physical fitness grades, and dozens of states have adopted the BMI-snitching Fitnessgrams, which are marketed by an outfit called the Cooper Institute. The group contracts with New York, Texas, California and a total of nearly 70,000 schools across the country to provide training, administration, data collection and dissemination of its reports. Big Brother is big business.

One of the Cooper Institute’s most prominent members of its board of directors: Big Government Republican Mike Huckabee, who spearheaded mandatory student BMI reports in 2003 while he was governor of Arkansas.

Huckabee has sided with first lady Michelle Obama’s meddling initiatives on childhood obesity — which he calls an “issue of national security.” Public health bureaucrats use exactly such hyperbolic rhetoric to justify increasing their powers, budgets and control.

Riding the manufactured obesity-crisis wave, BMI report card promoters are pushing for far more radical data-mining intrusion. A little-noticed study published in the journal Health Affairs a few years ago on “state surveillance of childhood obesity” proposes getting around federal family privacy protections by declaring obesity a “public health threat” at every state level. This would allow agencies to invoke “public health protection powers” to allow unfettered sharing of student BMI data.

These obesity police also advocate circumventing legislative debate by “simply adding a new function to state-run registries and databases” and slipping height and weight monitoring into immunization information-gathering systems.

Exploiting the captive student population for childhood obesity health research, grants, contracts and new tech boondoggles is yet another method of fattening Fed Ed’s overstuffed coffers.

It’s time for parents to opt out and put these government data gluttons on a diet.

Hands off.

Butt out.

Michelle Malkin is the author of “Culture of Corruption: Obama and his Team of Tax Cheats, Crooks and Cronies” (Regnery 2010).

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